Air conditioners installed in electric vehicles, hybrid vehicles, and so forth employ integrated-inverter electric compressors in which inverter devices are integrally built in. These integrated-inverter electric compressors are configured such that an inverter device, which converts DC power supplied from the on-board power to three-phase AC power, is integrally built into a housing of the electric compressor, and the compressor is driven by applying three-phase AC power converted by the inverter device to an electric motor accommodated in the housing.
Two power systems, a high-voltage power system for rotationally driving the electric motor and a low-voltage power system for control and communication, are connected to the inverter device. A control board used for the inverter device is configured so as to be correspondingly partitioned into a region in which a low-voltage circuit pattern is provided and a region in which a high-voltage circuit pattern is provided and so as to have a respective low-voltage-side ground region and a high-voltage-side ground region formed correspondingly to the circuit regions (for example, see PTLs 1 and 2).
In addition, because power lines, communication lines, and so forth are connected to the inverter device, electromagnetic noise is radiated from the outside through these lines. Because the inverter device includes high-voltage electronic components, such as semiconductor switching elements etc., the inverter device itself serves as a source of electromagnetic noise. In order to reduce the input/output of such electromagnetic noise, PTL 1 discloses a control board and a control device in which a patterned low-voltage-side ground is directly grounded to the casing (frame), a high-voltage-side ground is grounded to the casing (frame) through a capacitance element, such as a capacitor etc., and the low-voltage-side ground region and the high-voltage-side ground region are connected through the capacitor.